In recent years, various kinds of information are digitized, and are provided through the Internet or other environments. Under these circumstances, there are systems that utilize these environments to acquire attribute information on users, and provide services suitable for the individual users.
However, there are increasing problems of leakage of information such as personal information handled in these systems, or confidential information that companies have. For example, Patent Document 1 listed below discloses a system that includes plural data providers, data users, and a trusted third party (TTP). In this system, plural personal data provided by the plural data providers are distributed to data users in a manner such that each of the provided personal data does not include any personal indentifying information, and hence, can be recognized as data associated with each individual. With this system, it is possible to hide the identity of the personal data.